1. Field of the Invention
The present invention relates to preparation of mixtures rich in 6-chloro-2-trichloromethyl pyridine by non-catalytic liquid phase chlorination of alpha-picoline hydrochloride. Compositions enriched in 6-chloro-2-trichloromethyl pyridine are useful in agricultural applications, finding unusual application in soil culture, particularly in improving agricultural soil by retarding oxidation of ammonium ions in soil thereby improving plant nutrition therein.
2. Description of the Prior Art
The utility of 6-chloro-2-trichloromethyl pyridine as an oxidation retardant in soil is known, as in Goring U.S. Pat. No. 3,135,594. In addition, mixtures rich in 6-chloro-2-trichloromethyl pyridine and containing significant amounts of 3,6-dichloro and 5,6-dichloro-2-trichloromethyl pyridine, which are produced by the process of the subject invention, are known to be useful as raw materials in the production of 2,3,5,6-tetrachloropyridine and 2,3,4,5,6-pentachloropyridine which have known uses as herbicides and pesticides, and are also useful as chemical intermediates in the preparation of other highly desirable herbicides or pesticide products such as those described in Dietsche et al U.S. Pat. No. 4,256,894.
Previous methods for preparing mixtures rich in 6-chloro-2-trichloromethyl pyridine are described in Taplin U.S. Pat. Nos. 3,420,833 and 3,424,754, as well as The Dow Chemical Company Great Britain Pat. No. 957,276. In the examples of U.S. Pat. No. 3,424,754, yields of about 75% volatiles by weight of mixtures containing about 90% 6-chloro-2-trichloromethyl pyridine by weight (giving a net yield of about 68% by weight of 6-chloro-2-trichloromethyl pyridine) are obtained by chlorinating pre-formed alpha-picoline hydrochloride fed into the vapor space above an initiator charge heated to a reaction temperature of 220.degree. C. In this process, an essential function of the initiator charge is to react with chlorine gas sparged into the reaction and generate HCl which is combined with the alpha-picoline in another vessel to form liquid picoline hydrochloride. Chlorine to alpha-picoline hydrochloride feed ratios of from about 1.7 to about 6.0 by weight are used in the examples of U.S. Pat. No. 3,424,754. William James Sell (J. Chem. Soc. Vol. 87, pp 799 et seq., (1905)) describes the chlorination of alpha-picoline hydrochloride at about 105.degree.-110.degree. C. in which the alpha-picoline hydrochloride is made by direct addition of anhydrous hydrogen chloride gas to alpha-picoline. U.S. Pat. No. 3,420,833 describes the production of mixtures rich in 6-chloro-2-trichloromethyl pyridine by reaction of alpha-picoline vapor with chlorine in the vapor phase at temperatures in excess of 400.degree. C. in the presence of an inert diluent. Such a process is necessarily quite energy intensive because all feeds and diluents must be vaporized. Johnston et al U.S. Pat. No. 3,418,323 describes a method of preparing 6-chloro-2-trichloromethyl pyridine by reacting chlorine with 2-trichloromethyl pyridine in the liquid phase at temperatures from 120.degree. C. to 135.degree. C. in the presence of ultraviolet light.